108 W. G. WOOLNOUGH. 



Between these main streams the country to the north of 

 the Stirling Range forms an area of internal drainage. Its 

 characteristics and the extraordinary abundance of salt 

 lakes have been described above. The intersection of the 

 range itself by broad valleys has also been mentioned. 

 Taking these two facts together, the origin of the entire 

 structure may be understood. The following probably 

 represents fairly accurately the sequence of events. 



Originally there flowed across the low-lying peneplain 

 from north to south a number of subparallel streams, each 

 entering the Southern Ocean, which extended far north of 

 its present limits, by an independent mouth. Uplift of the 

 Stilling Range commenced, and proceeded so slowly at 

 first as to permit the streams to keep their channels not 

 only cut to base-level, but fairly mature as well. Under 

 such conditions laterite was formed over the lowlands, 

 including the valleys through the range. After the latter 

 had attained almost its full altitude above the plains, a 

 sudden sharp movement completed the differential elevation 

 and the streams were cut off and "beheaded." 1 



It is extremely probable that the climate of the whole 

 of Australia was undergoing a gradual desiccation while 

 these changes were in progress. Be that as it may, it is 

 certain that the rainfall of the area was no longer sufficient 

 to enable the smaller streams to emulate their more 

 powerful neighbours the Gordon and Pallinup, and " turn 

 the flanks" of the range. 



It is worthy of note that the area thickly covered by salt 

 lakes extends as far east as The Pass; that is, the salt 

 lake area faces that portion of the range which is traversed 

 by deep valleys. East of Warrungup the salt lakes cease 

 to be conspicuous, and, coincidently, the highlands of the 

 range become continuous. In all probability there was an 



1 Vide suggestion of faulting of laterlite level. 



